fpga: microchip-spi: move SPI I/O buffers out of stack

As spi-summary doc says:
 > I/O buffers use the usual Linux rules, and must be DMA-safe.
 > You'd normally allocate them from the heap or free page pool.
 > Don't use the stack, or anything that's declared "static".

Replace spi_write() with spi_write_then_read(), which is dma-safe for
on-stack buffers. Use cacheline aligned buffers for transfers used in
spi_sync_transfer().

Although everything works OK with stack-located I/O buffers, better
follow the doc to be safe.

Fixes: 5f8d4a90 ("fpga: microchip-spi: add Microchip MPF FPGA manager")
Signed-off-by: Ivan Bornyakov <i.bornyakov@metrotek.ru>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20221230092922.18822-2-i.bornyakov@metrotek.ruSigned-off-by: Xu Yilun <yilun.xu@intel.com>

drivers/fpga/microchip-spi.c

@@ -42,46 +42,55 @@
 struct mpf_priv {
 	struct spi_device *spi;
 	bool program_mode;
+	u8 tx __aligned(ARCH_KMALLOC_MINALIGN);
+	u8 rx;
 };
 
-static int mpf_read_status(struct spi_device *spi)
+static int mpf_read_status(struct mpf_priv *priv)
 {
-	u8 status = 0, status_command = MPF_SPI_READ_STATUS;
-	struct spi_transfer xfers[2] = { 0 };
-	int ret;
-
 	/*
 	 * HW status is returned on MISO in the first byte after CS went
 	 * active. However, first reading can be inadequate, so we submit
 	 * two identical SPI transfers and use result of the later one.
 	 */
-	xfers[0].tx_buf = &status_command;
-	xfers[1].tx_buf = &status_command;
-	xfers[0].rx_buf = &status;
-	xfers[1].rx_buf = &status;
-	xfers[0].len = 1;
-	xfers[1].len = 1;
-	xfers[0].cs_change = 1;
+	struct spi_transfer xfers[2] = {
+		{
+			.tx_buf = &priv->tx,
+			.rx_buf = &priv->rx,
+			.len = 1,
+			.cs_change = 1,
+		}, {
+			.tx_buf = &priv->tx,
+			.rx_buf = &priv->rx,
+			.len = 1,
+		},
+	};
+	u8 status;
+	int ret;
+
+	priv->tx = MPF_SPI_READ_STATUS;
+
+	ret = spi_sync_transfer(priv->spi, xfers, 2);
+	if (ret)
+		return ret;
 
-	ret = spi_sync_transfer(spi, xfers, 2);
+	status = priv->rx;
 
 	if ((status & MPF_STATUS_SPI_VIOLATION) ||
 	    (status & MPF_STATUS_SPI_ERROR))
-		ret = -EIO;
+		return -EIO;
 
-	return ret ? : status;
+	return status;
 }
 
 static enum fpga_mgr_states mpf_ops_state(struct fpga_manager *mgr)
 {
 	struct mpf_priv *priv = mgr->priv;
-	struct spi_device *spi;
 	bool program_mode;
 	int status;
 
-	spi = priv->spi;
 	program_mode = priv->program_mode;
-	status = mpf_read_status(spi);
+	status = mpf_read_status(priv);
 
 	if (!program_mode && !status)
 		return FPGA_MGR_STATE_OPERATING;
@@ -186,12 +195,12 @@ static int mpf_ops_parse_header(struct fpga_manager *mgr,
 }
 
 /* Poll HW status until busy bit is cleared and mask bits are set. */
-static int mpf_poll_status(struct spi_device *spi, u8 mask)
+static int mpf_poll_status(struct mpf_priv *priv, u8 mask)
 {
 	int status, retries = MPF_STATUS_POLL_RETRIES;
 
 	while (retries--) {
-		status = mpf_read_status(spi);
+		status = mpf_read_status(priv);
 		if (status < 0)
 			return status;
 
@@ -205,32 +214,32 @@ static int mpf_poll_status(struct spi_device *spi, u8 mask)
 	return -EBUSY;
 }
 
-static int mpf_spi_write(struct spi_device *spi, const void *buf, size_t buf_size)
+static int mpf_spi_write(struct mpf_priv *priv, const void *buf, size_t buf_size)
 {
-	int status = mpf_poll_status(spi, 0);
+	int status = mpf_poll_status(priv, 0);
 
 	if (status < 0)
 		return status;
 
-	return spi_write(spi, buf, buf_size);
+	return spi_write_then_read(priv->spi, buf, buf_size, NULL, 0);
 }
 
-static int mpf_spi_write_then_read(struct spi_device *spi,
+static int mpf_spi_write_then_read(struct mpf_priv *priv,
 				   const void *txbuf, size_t txbuf_size,
 				   void *rxbuf, size_t rxbuf_size)
 {
 	const u8 read_command[] = { MPF_SPI_READ_DATA };
 	int ret;
 
-	ret = mpf_spi_write(spi, txbuf, txbuf_size);
+	ret = mpf_spi_write(priv, txbuf, txbuf_size);
 	if (ret)
 		return ret;
 
-	ret = mpf_poll_status(spi, MPF_STATUS_READY);
+	ret = mpf_poll_status(priv, MPF_STATUS_READY);
 	if (ret < 0)
 		return ret;
 
-	return spi_write_then_read(spi, read_command, sizeof(read_command),
+	return spi_write_then_read(priv->spi, read_command, sizeof(read_command),
 				   rxbuf, rxbuf_size);
 }
 
@@ -242,7 +251,6 @@ static int mpf_ops_write_init(struct fpga_manager *mgr,
 	const u8 isc_en_command[] = { MPF_SPI_ISC_ENABLE };
 	struct mpf_priv *priv = mgr->priv;
 	struct device *dev = &mgr->dev;
-	struct spi_device *spi;
 	u32 isc_ret = 0;
 	int ret;
 
@@ -251,9 +259,7 @@ static int mpf_ops_write_init(struct fpga_manager *mgr,
 		return -EOPNOTSUPP;
 	}
 
-	spi = priv->spi;
-
-	ret = mpf_spi_write_then_read(spi, isc_en_command, sizeof(isc_en_command),
+	ret = mpf_spi_write_then_read(priv, isc_en_command, sizeof(isc_en_command),
 				      &isc_ret, sizeof(isc_ret));
 	if (ret || isc_ret) {
 		dev_err(dev, "Failed to enable ISC: spi_ret %d, isc_ret %u\n",
@@ -261,7 +267,7 @@ static int mpf_ops_write_init(struct fpga_manager *mgr,
 		return -EFAULT;
 	}
 
-	ret = mpf_spi_write(spi, program_mode, sizeof(program_mode));
+	ret = mpf_spi_write(priv, program_mode, sizeof(program_mode));
 	if (ret) {
 		dev_err(dev, "Failed to enter program mode: %d\n", ret);
 		return ret;
@@ -274,11 +280,9 @@ static int mpf_ops_write_init(struct fpga_manager *mgr,
 
 static int mpf_ops_write(struct fpga_manager *mgr, const char *buf, size_t count)
 {
-	u8 spi_frame_command[] = { MPF_SPI_FRAME };
 	struct spi_transfer xfers[2] = { 0 };
 	struct mpf_priv *priv = mgr->priv;
 	struct device *dev = &mgr->dev;
-	struct spi_device *spi;
 	int ret, i;
 
 	if (count % MPF_SPI_FRAME_SIZE) {
@@ -287,18 +291,18 @@ static int mpf_ops_write(struct fpga_manager *mgr, const char *buf, size_t count
 		return -EINVAL;
 	}
 
-	spi = priv->spi;
-
-	xfers[0].tx_buf = spi_frame_command;
-	xfers[0].len = sizeof(spi_frame_command);
+	xfers[0].tx_buf = &priv->tx;
+	xfers[0].len = 1;
 
 	for (i = 0; i < count / MPF_SPI_FRAME_SIZE; i++) {
 		xfers[1].tx_buf = buf + i * MPF_SPI_FRAME_SIZE;
 		xfers[1].len = MPF_SPI_FRAME_SIZE;
 
-		ret = mpf_poll_status(spi, 0);
-		if (ret >= 0)
-			ret = spi_sync_transfer(spi, xfers, ARRAY_SIZE(xfers));
+		ret = mpf_poll_status(priv, 0);
+		if (ret >= 0) {
+			priv->tx = MPF_SPI_FRAME;
+			ret = spi_sync_transfer(priv->spi, xfers, ARRAY_SIZE(xfers));
+		}
 
 		if (ret) {
 			dev_err(dev, "Failed to write bitstream frame %d/%zu\n",
@@ -317,12 +321,9 @@ static int mpf_ops_write_complete(struct fpga_manager *mgr,
 	const u8 release_command[] = { MPF_SPI_RELEASE };
 	struct mpf_priv *priv = mgr->priv;
 	struct device *dev = &mgr->dev;
-	struct spi_device *spi;
 	int ret;
 
-	spi = priv->spi;
-
-	ret = mpf_spi_write(spi, isc_dis_command, sizeof(isc_dis_command));
+	ret = mpf_spi_write(priv, isc_dis_command, sizeof(isc_dis_command));
 	if (ret) {
 		dev_err(dev, "Failed to disable ISC: %d\n", ret);
 		return ret;
@@ -330,7 +331,7 @@ static int mpf_ops_write_complete(struct fpga_manager *mgr,
 
 	usleep_range(1000, 2000);
 
-	ret = mpf_spi_write(spi, release_command, sizeof(release_command));
+	ret = mpf_spi_write(priv, release_command, sizeof(release_command));
 	if (ret) {
 		dev_err(dev, "Failed to exit program mode: %d\n", ret);
 		return ret;